A document scanner receives light reflected from a document, and converts the image on the document into an electronic format for further processing. Digital scanners use digital photosensors that convert the light reflected from the document into digital electronic information. A lens may focus the document image onto the digital photosensors. Alternatively, the linear array of photosensors may extend across the entire width of the document to be scanned. The linear array of photosensors may be moved along the documents, or the document may be moved past the linear array of photosensors. In certain instances, it may be possible to scan the document using digital photosensors that move in a predetermined pattern, such as a raster format.
For accurate processing of a scanned document image, it is helpful to accurately control the relative positions of the optical elements, such as the lens and the photosensors, and the transport mechanism for moving the paper past the photosensors, or for moving the photosensors past the document to be scanned.